In the present study we have characterized the evolution of changes in systemic haemodynamics (thermodilution in conscious animals) and sodium balance (metabolic cages) in a model of liver cirrhosis induced by chronic bile duct ligation (BDL). Mean arterial pressure (BDL, 111.5+/-4.7 mmHg; sham-operated, 122.9+/-3.0 mmHg) and peripheral vascular resistance (BDL, 2.63+/-0.08 units; sham-operated, 2.93+/-0.09 units) were lower in BDL rats from day 12 after surgery and decreased progressively throughout the following days. Portal hypertension was evident earlier in BDL rats and was maintained throughout the study period. Cardiac index (BDL, 58.8+/-3. 9 ml.min(-1).100 g(-1); sham-operated, 43.9+/-1.5 ml.min(-1).100 g(-1)) and stroke volume (BDL, 147.2+/-12.7 ml.beat(-1).100 g(-1); sham-operated, 109.0+/-4.2 ml.beat(-1).100 g(-1)) were significantly elevated in the BDL rats only from day 18 after surgery. There were no significant differences in sodium balance between the groups until day 16 after surgery, at which time BDL animals started to retain significantly more sodium than the controls. Sodium retention increased progressively, and at day 20 BDL rats had retained 0.7 mmol/100 g more than the control animals (accumulated retention: BDL, 2.2+/-0.2 mmol/100 g; sham-operated, 1.5+/-0.2 mmol/100 g). Plasma renin activity and aldosterone concentration were not elevated in the BDL animals at days 12, 16 or 20 after surgery. These data indicate that the BDL rat model shows early portal hypertension, peripheral vasodilation and arterial hypotension, several days before sodium retention is detectable, and in the absence of changes in plasma levels of renin and aldosterone. Overall, these data suggest that, in the BDL rat model, sodium retention is secondary to portal hypertension and peripheral vasodilation.

In the present study, we have analysed the mechanisms of Ca(2+) entry and release in platelets obtained from BDL (bile-duct-ligated) rats, 11-13 days and 4 weeks after surgery. Platelets were washed and loaded with fura-2, and [Ca(2+)](i) (cytosolic Ca(2+) concentration) was determined in cell suspensions by means of fluorescence spectroscopy. Basal [Ca(2+)](i) was similar in platelets from BDL rats compared with those from their respective controls, both in the absence and presence of extracellular Ca(2+). Platelet stimulation with thrombin in the absence and presence of extracellular Ca(2+) induced a rapid rise in [Ca(2+)](i) that was of greater magnitude in platelets from BDL rats than in controls. Ca(2+) storage was significantly elevated in platelets from BDL rats, as well as the activity of SERCA (sarcoplasmic/endoplasmic-reticulum Ca(2+)-ATPase). Capacitative Ca(2+) entry, as evaluated by inhibition of SERCA with thapsigargin, was also altered in platelets from BDL rats, having lower rates of Ca(2+) entry. In conclusion, chronic BDL alters intracellular Ca(2+) homoeostasis in platelets, such that an enhanced Ca(2+) release is evoked by thrombin, which may be due to an increased amount of Ca(2+) stored in the intracellular organelles and secondary to an enhanced activity of SERCA. These alterations are already evident before cirrhosis has completely developed and occurs during the cholestasis phase.

A B S T R A C TThe mechanisms that mediate hyporesponsiveness to vasoconstrictors in liver cirrhosis are not completely established. In the present study we have explored the role of NO and potassium channels by studying the pressor response to methoxamine in rats with carbon tetrachlorideinduced cirrhosis with ascites. Experiments were performed in the isolated and perfused mesenteric arterial bed of control rats and of cirrhotic rats with ascites. Pressor responses to methoxamine, an α-adrenergic agonist, were analysed under basal conditions, after inhibition of guanylate cyclase with Methylene Blue (MB ; 10 µM), after inhibition of NO synthesis with N Gnitro-L-arginine (L-NNA ; 100 µM) and after blockade of potassium channels with tetraethylammonium (TEA ; 3 mM). Compared with those from controls, preparations from cirrhotic rats showed a lower pressor response to methoxamine (maximum : controls, 114.4p6.8 mmHg ; cirrhotic rats, 74.7p7.3 mmHg). Pretreatment with MB or L-NNA increased the responses in both groups, but without correcting the lower than normal response of the cirrhotic rats. Pretreatment with TEA alone did not modify the responses as compared with the untreated groups. Pretreatment with TEA plus MB or TEA plus L-NNA also potentiated the responses, and the responses of the cirrhotic animals were greater than those of the groups treated with MB or L-NNA alone. However, no treatment completely normalized the lower response of the mesenteries from cirrhotic animals, suggesting that factors other than NO and potassium channels also participate, although to a lesser degree, in the lower pressor response of the mesenteric arterial bed of animals with cirrhosis. These results confirm that NO and potassium channels are important mediators of the lower vascular pressor response of the mesenteric bed of cirrhotic rats with ascites. This effect seems to be mediated by the NO-dependent formation of cGMP and by the NO-dependent and -independent activation of potassium channels.

Background: In the present study we have analyzed the mechanisms of calcium entry and mobilization in platelets obtained from rats chronically treated with the nitric oxide synthesis inhibitor, N-nitro L-arginine methyl ester [L-NAME, 40 mg/kg/day, 5 days). The platelets were obtained the day of the experiment, washed and loaded with fura-2. The intracellular calcium levels were determined in suspension of cells by means of fluorescence spectroscopy.